MAX1459 Datasheet, PDF (11/24 Pages) Maxim Integrated Products – 2-Wire, 4-20mA Smart Signal Conditioner

2-Wire, 4–20mA
Smart Signal Conditioner
Data Input/Output
The DIO line is an input/output pin used to issue com-
mands to the MAX1459 (input mode) or read the
EEPROM contents (output mode).
In input mode (the default mode), data on DIO is
latched on each rising edge of SCLK. Therefore, data
on DIO must be stable at the rising edge of SCLK and
should transition on the falling edge of SCLK.
DIO will switch to output mode after receiving either the
READ EEPROM command or the READ EEPROM
MATRIX command. See the Read EEPROM section for
detailed information.
Communication Protocol
To initiate communication, the first 8 bits on DIO after
CS transitions from low to high must be 101010U0 (AA
hex or A8 hex, defined as the INIT sequence). The
MAX1459 will then begin accepting 16-bit control
words (Figure 4).
If the INIT SEQUENCE is not detected, all subsequent
data on DIO is ignored until CS again transitions from
low to high and the correct INIT SEQUENCE is received.
The U bit of the INIT SEQUENCE controls the updating
of the DACs and configuration register from the internal
EEPROM. If this bit is low (U = 0, INIT SEQUENCE = A8
hex), all four internal DACs and the configuration regis-
ter will be updated from the EEPROM on the next rising
edge of CS (this is also the default on power-up). If the
U bit is high (INIT SEQUENCE = AA hex), the DACs
and configuration register will not be updated from the
internal EEPROM; they will retain their current value on
any subsequent CS rising edge. The MAX1459 contin-
ues to accept control words until CS is brought low.
Control Words
After receiving the INIT SEQUENCE on DIO, the
MAX1459 begins latching in 16-bit control words, MSB
first (Figure 5).
The first 4 bits of the control word (the MSBs,
CM3–CM0) are the command field. The last 12 bits
(D11–D0) represent the data field. The MAX1459 sup-
ports the commands listed in Table 5.
No-OP Command (0 hex)
The no-operation (No-OP) command must be issued
before and after the commands ERASE EEPROM and
WRITE EEPROM BIT. In the case of the ERASE EEP-
ROM command, the control word must be 0000 hex. In
the case of the WRITE EEPROM BIT command, the
command field must be 0h, and the data field must
have, in its lower bits, the EEPROM address to be writ-
ten (Figure 6). For example, to write location 1C hex of
CS
SCLK
DIO
t_MIN = 1.5ms
8 CLK
CYCLES
16 CLK
CYCLES
16 CLK
CYCLES
n x 16 CLK
CYCLES
X
1 0 1 0 1 0 U 0 CM3 CM2 DO CM3 CM2 DO
INIT
SEQUENCE
CONTROL
WORD
CONTROL
WORD
CONTROL
WORDS
Figure 4. Communication Sequence
SCLK
COMMAND
MSB
LSB MSB
DATA
LSB
DIO CM3 CM2 CM1 CM0 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
16-BIT CONTROL WORD
MSB
LSB
Figure 5. Control-Word Timing Diagram
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